#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N = 10001;
const int INF = 1e9;
struct Tedge{
int v, w;
Tedge(int _v, int _w){
v = _v;
w = _w;
}
};
int n, k, x, dp[N][N][2], sz[N], tmpDp[N][2];
vector <Tedge> adj[N];
void minimize(int &x, const int &y){
if (x > y)
x = y;
}
void dfs(int u, int p){
sz[u] = 1;
for(int i = 1; i <= n; i++)
dp[u][i][0] = dp[u][i][1] = INF;
dp[u][1][0] = dp[u][1][1] = 0;
for(Tedge e : adj[u]){
int v = e.v;
int w = e.w;
if (v == p)
continue;
dfs(v, u);
for(int i = 1; i <= n; i++){
tmpDp[i][0] = dp[u][i][0];
tmpDp[i][1] = dp[u][i][1];
}
for(int a = 1; a <= sz[u]; a++)
for(int b = 1; b <= sz[v]; b++){
minimize(tmpDp[a + b][0], dp[u][a][1] + dp[v][b][0] + w);
minimize(tmpDp[a + b][0], dp[u][a][0] + dp[v][b][1] + 2 * w);
minimize(tmpDp[a + b][1], dp[u][a][1] + dp[v][b][1] + 2 * w);
}
sz[u] += sz[v];
for(int i = 1; i <= n; i++){
dp[u][i][0] = tmpDp[i][0];
dp[u][i][1] = tmpDp[i][1];
}
}
}
void readInput(){
cin >> n >> k >> x;
for(int i = 1; i < n; i++){
int u, v, w;
cin >> u >> v >> w;
adj[u].push_back(Tedge(v, w));
adj[v].push_back(Tedge(u, w));
}
}
void solve(){
dfs(x, -1);
cout << dp[x][k][0];
}
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
readInput();
solve();
return 0;
}
